Enhancement of specific heat of ternary nitrate (LiNO3-NaNO3-KNO3) salt by doping with SiO2 nanoparticles for solar thermal energy storage

An enhancement of specific heat in a ternary molten nitrate salt eutectic doped with nanoparticles at a minute concentration is reported. SiO₂ nanoparticles, whose nominal size is 60 nm, were doped into a ternary nitrate molten salt eutectic (LiNO₃-NaNO₃-KNO₃) at 1% concentration by weight. A modulated differential scanning calorimeter was employed to characterise the specific heat of the eutectic mixture. According to a density weighted specific heat model, the effective specific heat of the mixture should not significantly change since the concentration of the nanoparticles is very small. However, the specific heat of the mixture of eutectic and nanoparticles was enhanced by 13%. From a subsequent material characterisation, a large amount of fractal-like nanostructure formation by the eutectic near embedded SiO₂ nanoparticles was observed. The nanostructure has a very large specific surface area as have the embedded SiO₂ nanoparticles. This can significantly amplify the effect of surface energy on the effective specific heat and is thus responsible for the enhanced specific heat of the mixture. Using the ternary molten salt eutectic with enhanced specific heat for thermal energy storage can significantly increase the energy storage efficiency and thus reduce the cost of electricity in a concentrated solar power system.